1. Field of the Invention
The present invention relates to a transmission control system that controls operations of actuators for moving a shift arm of a transmission so as to position the shift arm at a predetermined target position.
2. Description of the Related Art
As a transmission mounted in a vehicle, there has been known, for example, an automatic/manual transmission (AMT) that includes actuators, such as motors, to perform a selecting operation and a shifting operation of a manual transmission (MT) that transmits motive power between an input shaft and an output shaft of a vehicle when a driver manually carries out the selecting and shifting operations.
The present inventors have proposed a control system for performing a shifting operation of an automatic/manual transmission by adopting response specifying control in the previous application, namely, Japanese Laid-Open Patent Publication No. 2004-211717. In the control system, a coupling sleeve that integrally rotates with an input shaft is moved into contact with a synchronized gear through the intermediary of a synchronizer ring, and the coupling sleeve and the synchronized gear are rotationally synchronized to perform the shifting operation.
The response specifying control is conducted by determining a manipulated variable for driving actuators so as to converge the value of a switching function to zero. The switching function is defined by a linear function based on the difference between a target position and an actual position of a coupling sleeve. A computing coefficient of the linear function is set to lower disturbance suppressing capability level so as to produce a compliance property, which is resiliency of rubber or the like, thereby damping contact impacts when the coupling sleeve comes into contact with the synchronizer ring.
There has been also proposed a control system featuring improved stability of sliding mode control by limiting a model parameter identification range when identifying a model parameter in a model equation of a control object that changes due to deterioration with age or disturbance, thus restraining the occurrence of drift of a model parameter (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-15703).
An automatic/manual transmission control system calculates a target value Psl_cmd of a position Psl in the selecting direction and a target value Psc_cmd of a position Psc in the shifting direction of the shift arm involved in the selecting operation and the shifting operation in response to a speed change command to conduct positioning control by a selection controller that controls the operation of a selection actuator such that Psl agrees with Psl_cmd. Further, the positioning control is carried out by a shift controller that controls the operation of a shift actuator such that Psc agrees with Psc_cmd.
In a conventional automatic/manual transmission control unit, the response specifying control has been used to control the shift actuator by a shift controller. FIGS. 28A and 28B illustrates displacements of the shift arm when the shifting operation of the transmission is performed by the conventional shift controller. The axes of ordinates in the upper graphs indicate target position Psc_cmd and actual position Psc of the shift arm in the shifting direction, while the axes of ordinates in the lower graphs indicate control input Vsc to be supplied to the shifting actuator. The axes of abscissas indicate time t.
FIG. 28A shows a case where the dynamic characteristic of a transmission is within a standard range predicted beforehand when the shift controller was designed. FIG. 28B shows a case where the transmission has a low friction and a low reactive force at rotational synchronization, the dynamic characteristic of the transmission being out of the standard range. Referring to FIG. 28A, x10 denotes a target position Psc_cmd, y10 denotes an actual position Psc, and z10 denotes a control input Vsc. Referring to FIG. 28B, x11 denotes a target position Psc_cmd, y11 denotes an actual position Psc, and z11 denotes a control input.
FIG. 28A indicates that the actual position Psc (y10) stably converges to the target position Psc_cmd (x10) even if the target position Psc_cmd (x10) suddenly increases at t102 and t103. In contrast, FIG. 28B indicates that when a sudden increase takes place in the target position Psc_cmd (x11) at t112 with a resultant increase in the control input Vsc (z11), an undue pushing force causes a coupling sleeve to be pushed into a synchronizer ring because of the low friction. This inconveniently produces an inertial force change shock attributable to a sudden rotational synchronization.
Furthermore, when the target position Psc_cmd (x11) is changed to Psc_end at t113, the control input Vsc (z11) rapidly increases, causing the actual position Psc (y11) to overshoot the target position Psc_end. This in turn causes the coupling sleeve to collide with a stopper, inconveniently producing a colliding noise, which is uncomfortable to a driver.
A problem also arises when the response specifying control is used to control a selection actuator by a selection controller. FIG. 29 shows a displacement of the shift arm when the shifting operation of a transmission is performed by a conventional selection controller. The axis of ordinates indicates target position Psl_cmd of the shift arm in the selecting direction and actual position Psl, while the axis of abscissas indicates time t.
Referring to FIG. 29, x12 denotes a target position Psl_cmd of the shift arm in the selecting direction, y12 denotes an actual position Psl of the shift arm when the dynamic characteristic of the transmission remains within the aforesaid standard range, z12 denotes the actual position Psl when the transmission has a dynamic characteristic that is out of the standard range and has a low friction, and u12 denotes the actual position Psl of the shift arm when the transmission has a dynamic characteristic that is out of the standard range and has a high friction.
In the case of y12 when the dynamic characteristic remains within the standard range, when the target position Psl_cmd (x12) changes from Psl_cmd50 to Psl_cmd51 at t120, the actual position Psl quickly converges to the new target position Psl_cmd51. In the case of Z12 with the low friction, the actual position Psc overshoots the target position Psl_cmd51, and the overshoot causes a vibration, inconveniently prolonging the time of convergence to the target position Psl_cmd51. In the case of u12 with the high friction, the moving speed of the shift arm decrease, also inconveniently prolonging the time of convergence to the target position Psl_cmd51.